Apparatus, and a related method, for eliminating the effect of speckle images caused by surface imperfections in a primary mirror of a stellar coronagraph. Depending on their size, mirror imperfections can result in speckles in a field of view that also includes an image of a distant target planet. By generating a traveling surface wave in the mirror surface, and then tuning the spatial wavelength of the surface wave to approximately match that of a surface imperfection, the speckle image corresponding to that surface imperfection is made to twinkle in irradiance. Tuning the traveling surface wave though a wide range of spatial wavelengths causes each speckle image in turn to be identified by twinkling, while the target planetary image remains unvarying. Accordingly, multiple speckles corresponding to different mirror imperfections may be conveniently eliminated by image processing.